The present invention relates to a backflow prevention valve attached to a tip of a fuel supply pipe for supplying fuel to a fuel tank of an automobile. The backflow prevention valve is usually closed to prevent backflow of the fuel, so that when the automobile turns over or falls down, the fuel does not leak from the supply pipe. When the fuel is supplied to the fuel tank, a fuel liquid pressure opens the backflow prevention valve for the fueling.
As shown in FIG. 7, a backflow prevention valve v is attached to a tip of a supply pipe p for supplying fuel into a fuel tank t of an automobile in order to prevent the fuel from leaking through the supply pipe p when the automobile turns over or falls down.
As shown in FIGS. 8(A) and 8(B), a conventional backflow prevention valve has been disclosed in Japanese Patent Publication (Tokkai) No. 11-78549. As shown in FIGS. 8(A) and 8(B), the backflow prevention valve is formed of a cylindrical case member a and a covering member b for closing a lower end of the case member. An inflow opening c is formed at an upper end of the case member, and a liquid inflow pipe d with a smaller diameter is connected to the inflow opening c. A valve member e is disposed inside the case member a to be movable for opening and closing the inflow opening c from inside.
The valve member e is formed of a cylindrical body, and has four guiding arms f formed on an upper peripheral surface of the cylindrical body at locations shifted by 90 degrees with each other. A conical projection g is projected at a center of a top surface of the valve member e for regulating the fuel flow, and a ring-shaped sealing portion h is provided at a lower peripheral edge.
The valve member e is disposed inside the case member a in a state that each guiding arm f is inserted in the liquid inflow pipe d, and is urged upward (toward the liquid inflow pipe d) by a coil spring i. Four guiding grooves j formed between a pair of projecting strips along an axial direction are provided on an inner surface of the liquid inflow pipe d at locations shifted by 90 degrees with each other. Each guiding arm f is fitted to slide inside each guiding groove j. The valve member e is supported and guided by the guiding arms f sliding inside the guiding groove j.
The backflow prevention valve is disposed in the fuel tank t, like the valve v shown in FIG. 7, when the liquid inflow pipe d is attached to an end of the supply pipe p of the fuel tank t. As shown in FIG. 8(A), the sealing portion h of the valve member e usually contacts the peripheral edge of the inflow opening c of the case member a from inside by an urging force of the coil spring i. Accordingly, the valve member e closes the inflow opening c, so that the fuel inside the fuel tank does not leak through the supply pipe p.
When the fuel is supplied, as shown in FIG. 8(B), the valve member e moves downward (toward the covering member b) against the urging force of the coil spring i by a pressure of the fuel supplied into the fuel tank through the liquid inflow pipe d from the supply pipe. Therefore, the inflow opening c of the case member a opens, so that the fuel flows into the case member a through the inflow opening c from the liquid inflow pipe d. Then, the fuel is supplied into the fuel tank from an outlet (not shown) provided on the peripheral wall of the case member a.
However, in the conventional backflow prevention valve, the valve member e does not move smoothly when the fuel is supplied.
In other words, in the conventional backflow prevention valve, the guiding grooves j for guiding the valve member e are provided inside the liquid inflow pipe d, and eight projecting strips forming the guiding grooves j are projected on the inner surface of the liquid inflow pipe d. Consequently, when the fuel is supplied, the fuel flow causes turbulence inside the liquid inflow pipe d, so that the valve member e does not move smoothly due to the turbulence when a large amount of fuel is supplied at a high speed. Also, due to the turbulence, the valve member e can be twisted or tilted, resulting in an unstable movement of the valve member e for closing the valve after the fueling.
The present invention is proposed in order to solve the above problems, and an object of the present invention is to provide a highly reliable backflow prevention valve. The backflow prevention valve is usually closed to prevent the fuel backflow, and also can be opened and closed reliably and stably during and after the fueling.
Further objects and advantages of the invention will be apparent from the following description of the invention.